WASHINGTON — Scientists at the Smithsonian Institution's National Zoo have revealed they reversed a vasectomy on an endangered horse to allow it to reproduce naturally — the first-known operation of its kind on an endangered species.

Veterinarians said Monday that the surgery was performed in October 2007 on a Przewalski horse named Minnesota.

Luis Padilla, the zoo veterinarian who performed the reversal surgery, said the procedure was a first for this species and likely for any endangered species.

The horses are native to China and Mongolia and were declared extinct in the wild in 1970. Since then several hundred have been bred and reintroduced to the wild in Asia.

"This is kind of interesting turnaround," said Dr. Sherman Silber, a St. Louis urologist who pioneered reversible vasectomies in 13,000 humans and helped with the horse surgery. "We've made so much progress because the human really is the perfect model."

Will 'temporary vasectomy' become a fad?
A similar surgery was successfully performed while Padilla was a resident at the Saint Louis Zoo in 2003 on South American bush dogs, which resemble Chihuahuas. They are classified as vulnerable but not endangered.

Suzan Murray
/
National Zoo via AP

Zoo staff and a human urologist perform a reverse vasectomy for the second time on Minnesota after the first attempt was unsuccessful.

The "temporary vasectomy" could have a significant effect on how animals are managed in captivity by giving zookeepers a new way to control the animal's offspring without having to neuter them or use contraceptives that can change an animal's behavior.

Minnesota, the 20-year-old horse, had a vasectomy in 1999 at his previous home at the Minnesota Zoo. A vasectomy may be performed on an endangered animal because of space constraints, the size of species or if an animal has already produced many offspring and its genes are overrepresented in the population, said Budhan Pukazhenthi, a reproductive scientist at the National Zoo's Conservation and Research Center in Front Royal, Va.

Scientists later realized Minnesota was one of the most genetically valuable horses in the North American breeding program based on his ancestry. Zookeepers hope to find a suitable female for Minnesota in July.

Cheryl Asa, director of the American Zoo and Aquarium Association's Wildlife Contraception Center, said the reversible vasectomy could be useful in isolated cases but probably won't be adopted broadly.